"Could not find the main class"

Hello,
I am very new to java and recently attempted to run my first program. I created a simple program I found online in notepad

Code:

---

class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

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I saved this as "HelloWorldApp.java" and then went to my command prompt, went to the correct location, complied it using "javac HelloWorldApp.java", made sure the "HelloWorldApp.class" file was present, and then attempted to run the program by typing "java HelloWorldApp". This gave me an error saying

Quote:

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C:\Documents and Settings\Chris\My Documents\School>java HelloWorldApp
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorldApp
Caused by: java.lang.ClassNotFoundException: HelloWorldApp
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: HelloWorldApp. Program will exit.

---

I don't know what to do to fix this issue. I have found similar issues being fixed by changing the Environmental Variables, but I already changed the PATH and CLASSPATH to "C:\Program Files\Java\jdk1.6.0_21\bin".

Any help would be greatly appreciated!

First let me congratulate you on an excellent posting of your question.

If the HelloWorldApp.class file was in the School folder then the java command should find it.
Your CLASSPATH environment variable shouldn't refer to the JDK's bin folder. Either delete that variable or add to it the current folder (do that with a .) For example:
CLASSPATH=D:\JavaDevelopment;.

To see your current settings, open a command prompt window and enter: Set
If you want to copy the contents of that window:
To copy the contents of the command prompt window:
Click on Icon in upper left corner
Select Edit
Select 'Select All' - The selection will show
Click in upper left again
Select Edit and click 'Copy'

Paste here.

try

Code:

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Java -cp . HelloWorldApp

---

Add

Code:

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.;

---

to your CLASSPATH

The point checks the current directory.

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\Chris>Set
ALLUSERSPROFILE=C:\Documents and Settings\All Users
APPDATA=C:\Documents and Settings\Chris\Application Data
asl.log=Destination=file;OnFirstLog=command,enviro nment
CLASSPATH=.
CLIENTNAME=Console
CommonProgramFiles=C:\Program Files\Common Files
COMPUTERNAME=DELL-DESKTOP
ComSpec=C:\WINDOWS\system32\cmd.exe
FP_NO_HOST_CHECK=NO
HOMEDRIVE=C:
HOMEPATH=\Documents and Settings\Chris
LOGONSERVER=\\DELL-DESKTOP
NUMBER_OF_PROCESSORS=1
OS=Windows_NT
Path=C:\Program Files\Java\jdk1.6.0_21\bin;C:\Program Files\Java\jdk1.6.0_21\bin

PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WS F;.WSH
PROCESSOR_ARCHITECTURE=x86
PROCESSOR_IDENTIFIER=x86 Family 15 Model 2 Stepping 9, GenuineIntel
PROCESSOR_LEVEL=15
PROCESSOR_REVISION=0209
ProgramFiles=C:\Program Files
PROMPT=$P$G
QTJAVA=C:\Program Files\Java\jre6\lib\ext\QTJava.zip
SESSIONNAME=Console
SystemDrive=C:
SystemRoot=C:\WINDOWS
TEMP=C:\DOCUME~1\Chris\LOCALS~1\Temp
TMP=C:\DOCUME~1\Chris\LOCALS~1\Temp
USERDOMAIN=DELL-DESKTOP
USERNAME=Chris
USERPROFILE=C:\Documents and Settings\Chris
windir=C:\WINDOWS

Are you able to execute the class now with the java command?

I wonder why the path variable has the same path two times?

I am now able to run the program. Dipke's suggestion of using

Code:

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Java -cp . HelloWorldApp

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instead of

Code:

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java HelloWorldApp

---

worked. I did not change anything in the environmental variables, my CLASSPATH is still "C:\Program Files\Java\jdk1.6.0_21\bin", as is PATH. I am very appreciative of all the help you have both given me but I am still slightly confused on what environmental variables actually are and why some people have suggested adding "." or ".;" in the CLASSPATH. Any explanation would be greatly appreciated

Also, what is the difference between adding "-cp ." and just the plain "java" command. I have never seen "java -cp ." in any other literature before

I think you need to use the -cp . option to refer to the current directory because your CLASSPATH environ variable: "C:\Program Files\Java\jdk1.6.0_21\bin" does NOT include it.
I think the java command uses the CLASSPATH env var if given for the classpath. If it does not have the . for current directory, it does NOT look there.
If you delete the CLASSPATH env var, I think java will default to the current directory.

Okay, thanks a lot!

-cp is an abreviation for CLASSPATH.

This option (-cp .) adds the given path (.) to the current active CLASSPATH.
It is better to add the point to the CLASSPATH.
So java will search each time automaticily the current directory.

This issue is not written in every explanation of the CLASSPATH.

Kind regards